Moisture absorbent clays have historically been used as absorbent animal litters. Most clays used for animal litters are believed to contain smectites or other water-swellable clays, such as the polygorskite group clays, for liquid absorption. Smectite clays can increase several times by volume when absorbing water. This increase in volume can cause severe sewer damage when quantities of smectite clay are flushed down a toilet. Problems with moisture absorbent clays also include "dusting" upon pouring animal litters into a container and "mudding" upon urination of an animal into the clay. Controlling the volume fraction of fine material helps control the dusting and mudding problems. These "dust-free" animal litters have been enjoying an increased market share in recent years. However, breakage that occurs during shipping and handling typically produces a small amount of dust that can not be avoided.
When an animal urinates on a clay-based cat litter, a small pool of urine can quickly form on the top surface of the animal litter. The urine will subsequently soak into the animal litter and form a fairly large moist area. This moist area will tend to be avoided by cats upon subsequent visits to a litter box. Ammonia formed during the biological breakdown of the urine acts as a transfer agent of objectionable odors. Zeolites such as clinoptilolite have been mixed into some clay based animal litters for ammonia absorption to limit transfer of odors. The zeolite additions have been found to significantly reduce odors arising from the biological breakdown of urine.
For an animal litter to compete with clay based animal litters, it must possess good absorption characteristics, resistance to dusting and an acceptable bulk density. Several alternate materials have been proposed for use as animal litters. For example, Lojek et al., in U.S. Pat. No. 4,676,196, disclose a mixture of (limestone, alfalfa or other fibre material), (Portland cement or plaster of Paris) and a binder for holding the ingredients together. Bickoff et al., in U.S. Pat. No. 3,747,564, disclose use of a pressed, washed and dehydrated vegetative material as an animal litter. A combination of ferrous sulfate hepta-hydrate with fly ash or dried fine powders of zeolite for use as an animal litter is disclosed by Komakine in U.S. Pat. No. 3,776,188. R. F. Stockel, in U.S. Pat. No. 4,129,094, disclosed use of fly ash, bottom ash and/or boiler slag as a cat litter. As far as known, none of the above alternative animal litters have been able to successfully compete commercially with water-absorbent clay based animal litters.
It is an object of this invention to provide a clay-substitute animal litter that can match or exceed existing clay-based animal litters with regard to absorption characteristics, resistance to dusting and bulk density.
It is a further object of this invention to provide a animal litter that can reduce the volume of animal litter wetted during urination.